Giant Black Hole Likely Booted from Home Galaxy

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A supermassive black hole is apparently being ejected from its
host galaxy at a fantastic speed, suggesting that such
light-gobbling monsters may roam freely throughout the universe,
a new study reports.

The giant
black hole appears to have collided and merged with another
black hole. The newly supersized object then likely received a
powerful recoil kick from gravitational wave radiation that
booted it out into space at several million miles per hour,
researchers said.

"It's hard to believe that a
supermassive black hole weighing millions of times the mass
of the sun could be moved at all, let alone kicked out of a
galaxy at enormous speed," said study leader Francesca Civano, of
the Harvard-Smithsonian Center for Astrophysics (CfA), in a
statement.

"But these new data support the idea that gravitational waves —
ripples in the fabric of space first predicted by Albert Einstein
but never detected directly — can exert an extremely powerful
force," Civano added. [ Video:
Giant Black Hole Catapulted out of Galaxy ]

Telescope teamwork

The new study, which will be published in the June 10 issue of
The Astrophysical Journal, relies on observations made by a
variety of telescopes.

Using NASA's Hubble
Space Telescope, Civano and her team had previously spotted
two distinct sources of optical light in a system known as
CID-42, which is located in a galaxy about 4 billion light-years
from Earth. More optical data from two instruments in Chile
suggested that the two light sources are moving apart at a speed
of at least 3 million mph (5 million kph), researchers said.

NASA's Chandra space telescope had also detected a bright X-ray
source in CID-42, which was likely caused by super-heated
material around one or more gigantic black holes. But those
observations weren't quite detailed enough to give astronomers
the full story.

"The previous data told us that there was something special going
on, but we couldn't tell if there were two black holes or just
one," said co-author Martin Elvis, also of the CfA. "We needed
new X-ray data to separate the sources."

New Chandra observations have now confirmed that X-rays were
coming from only one of the sources, suggesting the following
scenario: Two galaxies collided, and the supermassive black holes
at their hearts merged.
Gravitational waves produced by the collision then booted
this hybrid black hole out into space.

But there are two other possible explanations for what's going on
in CID-42, researchers said. Three supermassive black holes in
the area may have had a run-in, causing the lightest one to be
ejected. Or CID-42 may contain two supermassive black holes that
are spiraling toward one another, rather than one zooming quickly
away.

However, both of those alternate explanations would require at
least one supermassive black hole to be heavily obscured, since
only one bright X-ray source is visible, so the Chandra data most
strongly support the idea of a black hole recoiling because of
gravitational waves.

Free-roaming black holes?

If the researchers' interpretation is correct, it could mean that
there are many supermassive black holes roaming unbound in the
vast stretches of intergalactic space.

And it could be tough to track these objects down.

"These black holes would be invisible to us, because they have
consumed all of the gas surrounding them after being thrown out
of their home galaxy," said co-author Laura Blecha, also of the
CfA.

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